java 多线程并行求和 之 join() 方法应用

现在 先看一个 继承Thread 类实现求和的java多线程并行程序如下：

package com.xing.add;
/**
 * 
 * @author LiuYinxing
 *
 */
public class And extends Thread{

	private long start;
	private long end;
	private long sum = 0;
	public And (long start, long end){
		super();
		this.start = start;
		this.end = end;
	}
	public void run(){
		for (long i = start; i <= end; i+=2)
			sum += i;
	}
	public long sum(){
		for (long i = start; i <= end; i++)
			sum += i;
		return sum;
	}
	public long getSum(){
		return sum;
	}
	public static void main(String[] args) throws InterruptedException{
		// TODO Auto-generated method stub
		And thread1 = new And(1, 1000000000);
		And thread2 = new And(2, 1000000000);
		long startTime = System.currentTimeMillis();
		thread1.start();
		thread2.start();
		thread1.join();
		thread2.join();
		long endTime = System.currentTimeMillis();
		System.out.println("并行结果 = " + (thread1.getSum() + thread2.getSum()));
		System.out.println("并行时间 = " + (endTime - startTime));
		
		startTime = System.currentTimeMillis();
		And serial = new And(1, 1000000000);
		long sum = serial.sum();
		endTime = System.currentTimeMillis();
		System.out.println("串行行结果 = " + sum);
		System.out.println("串行时间 = " + (endTime - startTime));
	}
}

运行结果如下：



我们可以看出线程

thread1.start();
		thread2.start();

在调用join()方法

thread1.join();
		thread2.join();

使其同时在多核上并行处理。由于其他的因素 加速比 700/420=1.666666667 虽然不等于2，但是并行的效果是显而易见的。